1. Field of the Invention
The present invention relates to a mixed gas turbine, in which a structure of a gas mixing section has been improved.
2. Description of the Prior Art
A mixed gas turbine is also called "mixed pressure turbine", and in the case where medium-pressure or low-pressure steam is excessive in a plant mainly in an industry-owned electric power generating plant of a paper manufactory, an industry-owned electric power generating plant for feeding both heat and electricity in an industrial complex, or the like, the excessive steam is introduced to an intermediate stage of a turbine to be effectively utilized as a power source for a low-pressure turbine. As the type of mixing gases, a type of connecting a gas-mixing pipe 14 provided with a mixed-gas stop valve 15 and a mixed-gas adjusting valve to a communication pipe 13 for connecting a high-pressure turbine casing 1 with a low-pressure turbine casing 11 as shown in a system diagram in FIG. 2, and a type where mixed-gas introduced from a mixed-gas pipe into a mixed-gas inlet B of a high-pressure turbine casing is received in a gas-mixing chamber C provided in a part of the casing 1 and after it has been mixed with exhaust gas from a final stage 3 of a high-pressure turbine, it is introduced to an initial stage 12 of a low-pressure turbine as shown in FIG. 3, are known.
In either one of these known types, in the case where a flow rate of steam flowing through the high-pressure turbine is large as compared to a flow rate of mixed-gas, a pressure loss caused by the mixed-gas adjusting valve is not large, and with respect to an efficiency, it does not become disadvantageous. In addition, even in the type shown in FIG. 3, since a step H between the high-pressure turbine final stage and the low-pressure turbine initial stage does not become so large, the structure would not become complex.
While the shortcomings such that an efficiency is deteriorated nor that a configuration of a turbine becomes complex does not occur in the case where a flow rate of steam flowing through a high-pressure turbine is large as compared to a flow rate of mixed-gas, the shortcomings would become remarkable under the following conditions:
1) When a flow rate in the high-pressure stage forming a main flow is small, a pressure at a mixed-gas joining section is low and a pressure difference from a source pressure on the mixed-gas feed side becomes large, these all result in pressure loss of a mixed-gas adjusting valve, and an efficiency is lowered.
2) In the case where a flow rate of mixed-gas is larger than a flow rate in the high-pressure stage, in relation to a flow passage area of a turbine blade lattice, a step of turbine disc diameters between a final stage of a high-pressure turbine and a first stage of a low-pressure turbine would become large, and so, a structure for compensating the step would become complex.